One important task of human syntactic parsing is the location of gaps (or "traces") and the linking of them to their fillers. The existing psycholinguistic work on the nature of these processes is both incomplete and conflicting. We propose a comprehensive, systematic investigation of gap-processing, focussing on adult normals' processing of WH-gaps, with the goal of developing a basic set of broad principles which can guide and constrain future efforts towards more detailed human parsing models (for normals, neurally-impaired patients, and children). Building on previous work, we formulate several specific questions concerning gap-processing and for each question outline a set of potential answers. We then propose psycholinguistic experiments which can provide evidence indicating the correct answer for each question. Important properties of these experiments are that, compared with the previous work, they utilize superior methodologies and test a wider range of materials. The particular questions addressed are: 1) What leads to the insertion of a gap into the syntactic representation being built for a sentence? 2) What properties characterize the parser's state of readiness for a gap? 3) Do gap-insertion processes obey Fodor's "Try-the-Next-Constituent" Principle? 4) Are gaps ever inserted at points not fully sanctioned by the grammar (e.g., parasitic gaps)? 5) Are gaps always immediately linked to their appropriate fillers? The results of the proposed work will bear on other questions concerning human language ability, such as the overall design principles of the parser (e.g., parallel vs. serial processing, immediate vs. delayed processing), the organization of the grammar, and the relation between parser and grammar. Additionally, because the experimental work often involves comparison of results from different paradigms, a much needed better understanding of the sensitivities of these paradigms will be attained. These supplementary outcomes of the work will be of direct utility for researchers in abnormal and child language.